Pedigrees were constructed from the family histories of all patients participating in the dementia program in order to examine the genetic basis of Alzheimer's disease. Collaborative studies were established to examine the ability of peripheral blood lymphocytes of probands with Down syndrome and familial Alzheimer's disease to repair X-irradiation induced damage during the G2 period of the cell cycle, and for the Down syndrome subjects, to see if the parents' lymphocytes show chromosomal instability. Efforts continue to evaluate genetic aspects of presenile dementia. Specifically, secondary sex chromosomal variation, alpha-l- antitrypsin (PI) phenotyping, and cytological analysis of variations in the Nucleolus Organizing Regions (NOR) were analyzed. Collaborative studies were established to address the questions of platelet membrane fluidity in Alzheimer's disease.